There is currently a great deal of interest in magnetoelectric multiferroic materials, attributable to the possible interactions between the material's magnetic and ferroelectric properties. This magnetoelectric coupling aids in the manipulation of magnetic properties using an electric field, as well as the converse. Of particular interest, from both a fundamental science as well as an applied technologies perspective, is the switching of magnetic domains by an electric field and vice versa. In this situation, the electric field is used to drive the system into a different orientation of the same ground state. The different ground state remains stable even in the absence of the electric field, and thus exhibits the basic requirements for nonvolatile data storage. One class of magnetic ferroelectrics is the BaMF4 family; where M=Mn, Fe, Co, or Ni. Such materials are known to be ferroelectric (i.e. exhibit reversible polarization) and to exhibit non-linear optical properties (i.e. frequency doublers for lasers). Two members of this family, namely BaCoF4 and BaNiF4, exhibit anti-ferromagnetic ordering at low temperatures. Such materials were originally synthesized utilizing a method that required high temperatures (e.g., 800° C.) under toxic conditions involving gaseous hydrofluoric acid.
Currently BaMF4 is synthesized through two related methods. The first involves heating BaF2 and MF2 (M=Mg, Mn, Co, Ni, or Zn) to temperatures above 800° C. in a HF (hydrofluoric acid) atmosphere using a horizontal zone-melting method. One drawback to this method is the use of gaseous HF which requires extensive precautions as it can cause severe damage if mishandled. For example, exposure to gaseous HF can cause extreme respiratory irritation, immediate and severe eye damage and pulmonary edema. Skin, eye, or lung exposure to concentrated (>50%) HF solutions will cause immediate, severe, penetrating burns. Exposure to less concentrated solutions may have equally serious effects, but the appearance of symptoms can be delayed for up to 24 hours. In addition, the horizontal zone-melting method is experimentally difficult.
A second known method for the synthesis of BaMF4 materials has been reported where BaF2 and MF2 (M=Mg, Mn, Co, Ni, and Zn) are melted in a platinum crucible at elevated temperatures (e.g., 800° C.), and crystals of BaMF4 are grown using the Bridgeman method. The Bridgeman method involves heating a polycrystalline material in a container—in this case, a platinum crucible—above its melting point and slowly cooling it from one end where a seed crystal is located. Single crystals are formed along the length of the container. Drawbacks to these methods include both the expense and experimental complexity. Thus, there exists a need for an inexpensive, effective and less hazardous method for the synthesis ferroelectric materials.